Presses for producing dimensionally stable pressed parts from powdered material essentially comprise a die, at least one upper punch and at least one lower punch which compress the powdered material from opposing sides in the cavity of the die. The upper and lower punches are, for example, connected to the ram and/or the piston rod of a hydraulic cylinder, which are attached to the press frame. The powdered material is introduced into the die bore by a suitable filling device, the position of the lower punch usually predetermining the filling height and/or the filling volume. After the pressing of the material, the pressed part is removed from the die bore.
Different designs are used with such presses. With so-called single-sided presses, the lower punch and the die are fixed. With double-sided presses, the die is either floatingly or forcibly moved with a fixed or movable lower punch. For removing the pressed part from the mould, either the so-called ejection method or the withdrawal method is used. With the ejection method, the pressed part is moved out of the stationary die by means of the lower punch, whilst with the withdrawal method, the lower punch is stationary and the die is moved.
The press tools are normally not directly attached to the hydraulic adjusting drives, but via so-called adaptors. Thus, for example, the die is clamped to a die holding plate which—if movable—is connected in turn to an adjusting drive by means of force transmission elements. The same applies to upper and lower punches which are attached to corresponding holding plates. As a result, different press tools may be fitted into an existing press.
In the prior art, a press is designed according to whichever principle is used for removal from the mould. A modification to the respective other principle for removal from the mould is, therefore, not normally considered.
For controlling and/or regulating a press process, information about at least two parameters is important. Firstly, the press force is measured in order to determine the maximum force with which the powder is compressed. The press force characteristic of the tools over the path and/or over time during the press process is also possibly useful. A further parameter is the position of the upper and lower punch with regard to a reference value, which is generally formed by the upper edge of the die. In the known manner, temperature effects and the press forces lead to alterations in the length of the press frame, the force transmission elements and the tools. By means of suitable measuring systems, the position of the tools may be measured via their adaptors but, without a correction of the respective temperature and press force, the position indications are not sufficiently accurate. In addition, there is the risk that the measuring systems themselves and/or the attachment thereof suffer temperature-related or press force-related deformation and, therefore, bring inaccuracies into the measurement.
A typical hydraulic press has been made known from DE 102 54 656 B4, the entire contents of which is incorporated herein by reference, in which a die holding plate and a plurality of punch carriers (adaptors) are adjustably mounted in the press frame via hydraulic drives. In the known press, support devices are provided which support the punch carriers in the final position of the press relative to the base body of the press frame. A press for producing stepped, dimensionally stable pressed parts made from ceramic powdered material has been made known from DE 3142126 B1, the entire contents of which is incorporated herein by reference, in which the receiver plates carrying the lower punch may be moved together hydraulically away from a base plate and, in the final position of the press, are positioned as receiving plates against adjustable mechanical stops of the base plate. The receiving plates may be raised together in steps for ejecting the pressed parts after withdrawing the die and releasing the peripheral surface of the pressed part which is in contact with the die, respectively until the next contact surface is released. In the final positions of the press formed by fixed stops, the counter force or supporting force is formed, in both presses, by mechanical stops.
A press has been made known from DE 103 00 722 B3, the entire contents of which is incorporated herein by reference, in which an upper and a lower slide carriage are vertically guided for attaching an upper and lower punch to a guide post. The guide post is fastened to a frame table to which the die holding plate is also attached. The holding plates are guided in a wear-free manner by attaching the sliding carriage to the hydraulic drive via an angle compensation element and a lateral compensation element.
The object of the invention is to provide a press for producing dimensionally stable pressed parts from powdered material, which allows a position identification of the tools with as few errors as possible.